ActionScript 3.0 Cookbook

Chapter 8. Bitmaps

Introduction

Flash 8 introduced the BitmapData class, one of the most important additions to the program at that time. Since its inception, Flash has been a vector-based tool. Vector graphics consist of mathematical descriptions of each graphical element. For example, a line starts at point x0, y0 and extends to point x1, y1. A bitmap, on the other hand, describes a graphic as a rectangular grid of values, with one color value assigned to each pixel.

The two main advantages of vector graphics are scaling and file size. When you scale a vector graphic, you are actually moving the points that make up the lines and curves of the graphic further apart or closer together. Thus, you can scale up or down to almost any size and still maintain smooth lines and curves. A bitmap, on the other hand, starts to look “blocky” as soon as you increase its size even slightly, since each pixel is simply made into a larger rectangle.

Since a vector graphic is nothing more than a list of coordinates that make up various lines, curves, and shapes, the file size tends to be quite low when compared to a bitmap graphic. Bitmap graphics, on the other hand, contain value information for each pixel in the image. For a 100×100-pixel image, this is a list of 10,000 individual values. Of course, most bitmap images use some form of compression to reduce the file size. Even so, they can be quite large.

The advantage of vector graphics went a long way to make Flash such a popular media format on ...